Voltage-current sensing system for welders and the like

ABSTRACT

This invention relates to a system for making a record of the amount of work actually produced by an arc welder or similar machine for a given period of time. The arc welder may be energized, for example, for eight hours but may be actually welding for only four or five hours. The system includes a current sensor which records only when at least minimum arc currents flow, and a voltage sensor which records only when at least voltages sufficient to sustain an arc and which are greater than those at which short circuit occur. The simultaneous occurrence of both such currents and voltages is necessary for recording.

Wenrich et a1.

1.4 1 Apr. 3, 1973 [54] VOLTAGE-CURRENT SENSING 3,359,561 12/1967Shostek ..219/135 SYSTEM FOR L ER AND THE 3,532,853 10 1970 MacKinney eta1. ....219 135 IK 2,366,548 1/1945 Oestreicher et a1. ..219/1352,027,224 1/1936 David ..219/135 [75] Inventors: Carl M. Wenrich,Readlng; Bernard W. Downs, Elverson, both of Pa. Primary Examiner Truhe[73] Assignee: Weld-Record Corporation, Elverson, Attorney-William Rum")R [22] Filed: May 6, 1971 [57] ABST ACT This invention relates to asystem for making a record [211 App! 140873 of the amount of workactually produced by an arc welder or similar machine for a given periodof time. [52] U.S. Cl ..219/136, 219/131 R, 219/137 The are welder maybe energized, for example, for [51] Int. Cl. ..B23k 9/00 i ht h u butmay be actually welding for only four [58] Field of Search ..219/131, orfi hours, The system includes a current sensor /1 317/60 1316- whichrecords only when at least minimum are cur- 346/33 33 MC, 33 31307/252 wrents flow, and a voltage sensor which records only when at leastvoltages sufficient to sustain an arc and [56] References cued which aregreater than those at which short circuit oc- UNITED STATES PATENTS cur.The simultaneous occurrence of both such currents and voltages 1snecessary for recording. 2,340,114 1/1944 Duis ..219/13 S 3,535,49110/1970 Krolski ..219/131 R 4 Claims, 1 Drawing Figure CABLE CONDUCTINGCURRENT TO OPERATION BEING MONITORED TlMEDi OR RECORDED. SUCH ASELECIRODE on WORK.

MAGNETIC MATERIAL OUTLET TERMINALS 0F WELDING,CUTTING,

OR GOUGING POWER SOURCE ELECTRICAL OUTLET SOCKET FOR AUXILIARYFUNCTIONS.

LE. A SINGLE PEN RECORDER TO PEN SOLENOID OF EVENT RECORDERVOLTAGE-CURRENT SENSING SYSTEM FOR WELDERS AND THE LIKE The presentinvention relates to a novel system for making a record of the amount ofwork produced by an arc welder or similar machine for any period oftime, sometimes referred to as its operating factor. For example, an arcwelder may be energized for 8 hours, but may be actually welding 4 or 5hours.

If industry could accurately determine the percentage of time duringwhich production welding occurs, a number of benefits would accrue. Thispercentage of arc-time is also referred to as Duty Cycle. The benefitsare as follows:

1. An accurate picture of relative productivity of individual welderscould be ascertained, thereby establishing an impartial means forrejection of personnel for cause or conversely rewarding good workers.

2. An accurate and impartial incentive payment plan could be set up inorder to voluntarily increase production.

3. An accurate means would be available to precisely determine costs onoperations not previously experienced, thereby making it much easier toquote accurately.

4. Where a different method or process is being considered for aparticular job, an accurate comparison can be made if the arc-time onlycan be segregated from all other phases of operations.

5. An unquestionable record of arc-time is needed which will overcomethe great deal of argument prevalent in many cases between productioncontrol and labor, as to the accuracy of the human being punching thestop watch, while trying to follow the on" and of timing of the arc.Many times, it is necessary for the re-study of an operation becauselabor questions the accuracy of stop watch timing of production welding.

A number of difficulties exist when one tries to determine actualproductive time.

1. There is a human tendency for an operator to try to defeat a systemwhich is used to evaluate him. Therefore, any such system needs to betamper-proof.

2. In many cases, when a single parameter, such as End of Stroke on apunch press is measured and used as a basis, the results are meaninglessbecause a press strokes just as effectively with parts in it as withoutparts in it. So, in this case, the presence of a part and a press strokeshould be required in order to record that stroke.

In the case of an arc welder, the machine could be made to delivercurrent into a relative short circuit, or to produce the propergenerator (power source) voltage level to record the presence ofwelding, without actually welding. However, if both parameters arerequired it becomes much easier to weld than to try to defeat a system.

An object of our invention, therefore, is to record production timewhile making difficult any attempts to defeat the recording system, byproviding a novel instrument which basically requires that two or moreinputs be present before the recording operation can take place.

Other objects and advantages will become more apparent from a study ofthe following description taken with the accompanying drawing wherein:

The single FIGURE is a circuit diagram of a voltagecurrent sensingsystem to record the actual welding time of an arc welder or the like.

Referring more particularly to the FIGURE, the secondary welding cable 1that conducts welding current to the electrode or work is passed througha device which senses the presence of magnetic flux around a conductorresulting from current passing through it. One way of doing this wouldbe to provide an encircling magnetic structure 2 formed of soft iron orother highly magnetic material. Any current in the cable 1 would providea magnetic field which would be concentrated by the high permeability ofthe iron. Soft iron is approximately two thousand times the magneticflux in the iron as there would appear in the same area in air. If a gapis provided in the encircling iron magnetic structure, and a suitablemagnetic reed switch 3 is posi tioned at that gap, then when weldingcurrent of sufficient magnitude flows, the reed switch 3 will close.This alone could operate a recorder. However, if the operator simplyshort circuited his electrode, he would produce sufficient current toclose the switch 3, thereby defeating the recording system.

When the operator short circuits his electrode, generator (power source)voltage is reduced below that which would be normal when an arc is beingheld or maintained.

Therefore, in accordance with the present invention there is providedanother sensing system in the instrument which measures the arc voltage.

When the operator is producing a normal arc, he has simultaneously thecorrect minimum welding current and the correct minimum arc voltage.Those two factors together simultaneously occuring turn on the recordinginstrument.

We have already described one basic method of sensing current.

When the reed switch closes, SCR-l of the instrument is turned on. ACpower (normal 1 15 volt AC Cycles) is allowed to proceed along thefollowing path, during the positive cycle, through diode D1, throughsilicon controlled rectifier SCR-l and diode D-5, and through diode D4to the recording instrument. On the reverse cycle, the flow is throughdiode D3, through rectifier SCR-l and diode D-5, and through diode D-2back to the AC power source l 15 volt AC 60 cycles).

Note that if rectifier SCR-1 is not turned on, there is an open circuit.During the positive cycle, diode D-l feeds diode D-3, which diodesoppose each other, thereby preventing current flow to the recorder.

The same situation exists with diodes D-2 and diode D-4, on the reversecycle. Note that when current flows in either the positive or reversecycle, it passes through rectifier SCR-1 in the same direction for bothconditions.

When the gate of an SCR(silicon controlled rectifier) is made morenegative than the cathode, the SCR will not conduct in either direction,but when the gate is made more positive than the cathode, the SCR turnson like a switch. The diode bridge, formed by diodes D-l, D-2, D-3 andD-4, provides that the anode of silicon controlled rectifier SCR-l bealways zero or positive, and never negative. If the anode of SCR-1 isconnected to the gate, whenever the junction of diodes D-l, D-3 risesabove zero, rectifier SCR-1 will turn on.

The gate of rectifier SCR-l cannot conduct safely as much current as theSCR could deliver, so current limiting resistors R-1 and R-2 are used toprevent heavy gate currents, thereby protecting the SCR when the reedswitch is closed. Diode D- is connected to junction of diodes D-2 andD-4, and to the cathode of SCR-1.

A diode, when conducting, has a relatively fixed voltage across it. Agermanium diode has approximately 0.2 of a volt drop across it, and asilicon diode has approximately 0.7 of a volt drop across it. Sincediode D-5 and rectifier SCR-l are in series, when rectifier SCR-l isturned off, there will be very little current flow, so a high resistanceR-4 is bridged across rectifier SCR-l so that a certain minimum ofcurrent will flow in diode D-5. The gate of rectifier SCR-l is connectedthrough resistor R-3 to the junction of diodes D-2, D-4 and D-S, whichjunction is at least 0.2 of a volt more negative than a cathode ofrectifier SCR-l. This bias is advisable so that dependable operation ofthe SCR is guaranteed. When the reed switch 3 is closed, the currentflowing through resistors R-1 and R-2, thence through resistor R3 willdevelop a voltage across resistor R-3 greater than 0.2 of a volt,turning rectifier SCR-1 on. Note that as soon as the gate becomespositive, the SCR turns on.

The voltage sensing circuit may be traced as follows. Since a weldingcurrent source can be either alternating or direct current, and a devicewhich is to turn on an SCR, should provide a positive polarity, a switchis provided in the form of a bridge network of diodes D1l, D-l2, D-l3and D-14. If a welding power source of any polarity were connected tothe junction of diodes D-ll and D-l2, and the junction of diodes D-13and D-14, current flows in the diodes and would provide that thejunction of diodes D-ll and D-l3 would always be positive with respectto the junction of diodes D-l2 and D-14.

Diode D-l6 is a special type of diode which offers a high resistance tothe flow of current in its inverse direction until a specific breakdownvoltage appears across it. At that time, the diode starts to drawcurrent and could, without some form of current limiting, be destroyed.A resistance, in this case, a ballast tube 5, is therefore placed inseries. A circuit is thus provided which will produce a voltage acrossdiode D-l6, resulting from a voltage impressed across the diode assemblyD-ll, D-l2, D-l3 and D-l4, from the welding power source.

The voltage across diode D-l6 will be proportional to the weldingcurrent source voltage, up to the time when the breakdown voltage ofdiode D-l6 is reached. Voltage across diode D-16 now remains constanteven though the welding source voltage increases. In this manner, D-l6provides that a maximum voltage will be present for the gate circuit ofSCR2, making it easier to provide that the allowable gate current forSCR 2 will not be exceeded.

The resistance of the ballast tube 5, when it is cold, is relatively lowand offers little hindrance to the current through diode D-16. As thecurrent through the ballast tube 5 increases after diode D-l6 starts toconduct, elements within the ballast tube become warm, thereby rapidlyincreasing in resistance and offering greater hindrance to currentthrough diode D-l6, thereby protecting the diode through a much widerrange of input voltage variation.

The circuit comprising rectifier SCR-2, diodes D-6, D-7, D-8, D-9 andD-l0 and resistors R-6 and R-S, is identical to the circuit whichincludes rectifier SCR-l, and the gate of rectifier SCR-2 is heldnegative through resistor R-S just as the gate of rectifier SCR-l washeld negative through resistor R3. In the absence of positive voltage onthe gate of rectifier SCR-2, there will be no current flow from thejunction of diodes D-6 and D-7, to the junction of diodes D-8 and D-9.Therefore, even if the'SCR-l circuit were conducting, the recordinginstrument would not be energized.

If SCR-l and SCR-2 circuits are both energized, the

AC power source volt AC 60 cycles) would be connected to the recordinginstrument.

Zener diode D-lS is selected so that its breakdown voltage, (the voltageat which it starts to conduct current), is just below that minimumvoltage required to maintain an arc.

if the output terminals of the welding current source are connected tothe diode bridge comprising diodes Dl1, D-l2, D-l3 and D-l4, there willbe no current in resistor D-S until the current source voltage is equalto or greater than the breakdown voltage of diode D-lS.

Resistor R-S is selected so that the current through diode D-lS will belimited to a value that can be safely conducted by diode D-15. It isevident that when the welding current source voltage is equal to thenecessary are voltage and when there is sufficient welding current toclose the reed switch 3, the recorder will operate. If either current orvoltage is incorrect, the recorder will not operate.

The ballast tube and diode D-l6 provide protection for diode D-l5 andresistor R-S, as the voltage across diode D-16 is regulated to a safemaximum by the action of the ballast tube 5 and diode D-l6, aspreviously described.

It should be noted that the voltage-current sensing system of thepresent invention is useful on all production electric welding, gougingand cutting applications or non-production operations thereof.Furthermore, it is applicable to AC or DC (constant current or constantvoltage) power sources (machines). Such power sources may be motorgenerator DC sources or rectifier DC sources.

While we have illustrated and described a single specific embodiment ofour invention, it will be understood that this is by way of illustrationonly and that various changes and modifications may be contemplatedwithin the scope of the following claims.

We claim:

1. In combination with an arc welder having a power source and a cablethat conducts welding current, a core of magnetic material magneticallycoupled to said cable, a switch immediately adjacent said core and whichcloses in response to a predetermined value of magnetic flux induced insaid core by said cable in response to welding current flow through saidcable, an AC source of power, a recorder, first and second full waverectifying bridge circuits connected in series between said AC source ofpower and said recorder, each rectifying bridge including four diodes inthe' respective four legs of the bridge circuit and a silicon controlledrectifier connected in the direct current to conduct current in theoutput leg upon actuation of the gate of the silicon controlledrectifier, output leg of each bridge circuit means responsive to theclosing of said switch for actuating the gate of the silicon controlledrectifier of the first bridge circuit, a third diode full wave rectifierhaving input terminals connected to sense the voltage output of thewelding power source and input terminals output, and means responsive toa predetermined voltage at said output terminals for actuating the gateof the silicon controlled rectifier of the second bridge circuit,whereby a circuit to said recorder will be completed only uponsimultaneous occurrence of predetermined values of welding current andvoltage.

2. A system as recited in claim 1 wherein said switch responsive towelding current is a reed switch, and

wherein said core is partially looped about said cable, therebyproviding an air gap adjacent which said first mentioned switch isplaced.

3. A system as recited in claim 1 wherein said voltage responsive meanscomprises a zener diode interconnecting said third rectifier and saidlast mentioned gate.

4. A system as recited in claim 3 further comprising a ballast tube inseries with said zener diode and one of the terminals of said thirdrectifier, and wherein a second zener diode together with said ballasttube are serially bridged across the output terminals of said thirdrectifier.

1. In combination with an arc welder having a power source and a cablethat conducts welding current, a core of magnetic material magneticallycoupled to said cable, a switch immediately adjacent said core and whichcloses in response to a predetermined value of magnetic flux induced insaid core by said cable in response to welding current flow through saidcable, an AC source of power, a recorder, first and second full waverectifying bridge circuits connected in series between said AC source ofpower and said recorder, each rectifying bridge including four diodes inthe respective four legs of the bridge circuit and a silicon controlledrectifier connected in the direct current to conduct current in theoutput leg upon actuation of the gate of the silicon controlledrectifier, output leg of each bridge circuit means responsive to theclosing of said switch for actuating the gate of the silicon controlledrectifier of the first bridge circuit, a third diode full wave rectifierhaving input terminals connected to sense the voltage output of thewelding power source and input terminals output, and means responsive toa predetermined voltage at said output terminals for actuating the gateof the silicon controlled rectifier of the second bridge circuit,whereby a circuit to said recorder will be completed only uponsimultaneous occurrence of predetermined values of welding current andvoltage.
 2. A system as recited in claim 1 wherein said switchresponsive to welding current is a reed switch, and wherein said core ispartially looped about said cable, thereby providing an air gap adjacentwhich said first mentioned switch is placed.
 3. A system as recited inclaim 1 wherein said voltage responsive means comprises a zener diodeinterconnecting said third rectifier And said last mentioned gate.
 4. Asystem as recited in claim 3 further comprising a ballast tube in serieswith said zener diode and one of the terminals of said third rectifier,and wherein a second zener diode together with said ballast tube areserially bridged across the output terminals of said third rectifier.